You Will 'Nut' Believe It: Nut Consumption Decreases Total and Cause-Specific Mortality
April 1, 2014
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Mortality
Abstract & Commentary
You Will 'Nut' Believe It: Nut Consumption Decreases Total and Cause-Specific Mortality
By Melissa Quick, DO, and David Kiefer, MD
Dr. Quick is a third-year resident in New York at the Beth Israel Residency in Family Medicine.
Dr. Quick reports no financial relationships relevant to this field of study.
Synopsis:This article examines the association of nut consumption with total and cause-specific mortality by evaluating two large, independent cohort studies of nurses and other health professionals.
Source:Bao Y, et al. Association of nut consumption with total and cause-specific mortality. N Engl J Med 2013;369:2001-2011.
Summary Points
- Nuts (peanuts and tree nuts) are unique, nutrient-dense foods rich in unsaturated fatty acids, fiber, vitamins, minerals, and many bioactive substances.
- Nut consumption is inversely associated with total mortality among women and men with greatest benefit seen when consuming nuts seven or more times a week.
- Scientific evidence suggests that nuts are a cardioprotective food.
Previous studies have suggested that nut consumption has multiple beneficial health effects, specifically in decreasing coronary heart disease.1,2 In this article, Bao et al sought to further examine the effect of nut consumption on mortality by examining extensive dietary data juxtaposed with 30 years of follow-up.
Two studies were analyzed: the Nurses' Health Study (NHS), a prospective cohort study that started in 1976 consisting of 121,700 female nurses from 11 U.S. states, and the Health Professionals Follow-up Study (HPFS), a prospective cohort study of 51,529 male health professionals from all 50 states that began in 1986. Of the enrolled participants, 76,464 women in the NHS and 42,498 men in the HPFS remained after excluding women and men with a history of cancer, heart disease, and stroke, or participants who did not provide adequate information about nut consumption or sufficient anthropometric data.
Information was collected via validated food-frequency questionnaires that were sent every 2-4 years, beginning in 1980 for the NHS and in 1986 for the HPFS. Participants were asked how often they had consumed a serving of nuts (serving size: 28 g [1 oz]) during the preceding year and were given the choices: never or almost never, one to three times a month, once a week, two to four times a week, five or six times a week, once a day, two or three times a day, four to six times a day, or more than six times a day. As the study went on, the wording of the questionnaire changed slightly as participants were asked the same question but with two discrete nut categories consisting of "peanuts" vs "other nuts." "Total nut" consumption was defined as the intake of peanuts and other nuts. Additional questionnaires were sent every 2 years to update medical and lifestyle information.
The primary endpoint of this analysis was death from any cause. Using systematic searches of individual states' vital records and the National Death Index, the authors were able to obtain 98% of death information in each cohort.
Data analysis was adjusted to minimize within-person variation, such as altered dietary patterns before or after a diagnosis of a major illness. Additionally, other data analysis modifications were made to reduce the influence of smokers, diabetics, or those with an extreme body mass index (BMI) — participants were excluded from the analysis if they had ever smoked, had a BMI < 18.5 kg/m2 or > 40 kg/m2, or had a diagnosis of diabetes at baseline.
Inverse associations were observed between nut consumption and most major causes of death, including heart disease, cancer, and respiratory diseases. In the NHS, the authors found during 30 years of follow-up (2,135,482 person-years), there were 16,200 total deaths. For the HPFS, after 24 years of follow-up (903,371 person-years), there were 11,229 documented deaths.
With pooled data from both cohorts in comparison to participants who did not eat nuts, those who consumed nuts less than once a week had a 7% lower death rate (hazard ratio [HR], 0.93; 95% confidence interval [CI], 0.90-0.96); for nut consumption once per week there was an 11% lower death rate (HR, 0.89; 95% CI, 0.86-0.93); for nut consumption two to four times per week a 13% lower death rate (HR, 0.87; 95% CI, 0.83-0.90); for nut consumption five to six times per week a 15% lower death rate (HR, 0.85; 95% CI, 0.79-0.91). Finally, those who consumed nuts seven or more times per week had a 20% lower death rate (HR, 0.80; 95% CI, 0.73-0.86; P < 0.001).
A separate analysis between peanuts and tree nuts displayed similar associations with total and cause-specific mortality between the two types of nuts. When consumption of nuts two or more times per week was compared with no nut consumption, the pooled multivariate-adjusted HRs for death were 0.88 (95% CI, 0.84-0.93) for peanuts and 0.83 (95% CI, 0.79-0.88) for tree nuts.
Commentary
It was only about 20 years ago that nuts were propelled from the "unhealthy" to the "healthy" food category, as their high fat content and high caloric value was unappealing to many consumers. Today, nuts are emerging as one of the most unique, nutrient-dense foods that exists by virtue of their distinctive combination of complex matrices rich in unsaturated fatty, fiber, vitamins, minerals, and multiple bioactive compounds.3 A common misconception is that foods high in fatty acids, such as nuts, can lead to excess weight gain. However, multiple studies have shown that there is no association between nut consumption and weight gain, and some research suggests nuts can actually help individuals lose weight.4,5
In the last decade, nuts have been gaining popularity in both the media and in the health care realm. In 2003, the FDA deemed nuts "heart healthy" and authorized the claim that "scientific evidence suggests but does not prove that eating 1.5 ounces (43 g) per day of most nuts as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease."6 Furthermore, multiple epidemiological and clinical studies have shown that frequent nut consumption is associated with improved plasma lipid profiles and decreased risk of coronary heart disease, certain types of cancer, stroke, atherosclerosis, type 2 diabetes, inflammation, and other chronic diseases.7,8
Indeed, Bao's study showed that the more a person ate nuts, the less he/she died from most major causes of death, including heart disease, cancer, and cardiovascular diseases. In terms of overall nut consumption, the following causes of death were significantly decreased regardless of quantity of nut consumption: "all causes" (P < 0.001), "cancer" (P = 0.03), "cardiovascular disease" (P < 0.001), and "heart disease" (P < 0.001). For each of these categories, there was an inverse association between amount of nuts eaten and the hazard ratio. The other causes of death did not have consistent inverse associations, nor were the results significant.
With regard to nut-specific results, only two categories of death — all-cause mortality and heart disease — displayed definitive positive effects (meaning a hazard ratio < 1 and a confidence interval not crossing 1) for each type of nut ("any nut," "peanut," or "tree nut"). For cancer as a cause of death, the results were only significant for those who ate "any nut" or "tree nuts." For respiratory disease as a cause of death, results were only significant for those who ate "peanuts."
Overall, these findings are quite promising, and they echo the findings of a recent landmark, randomized, primary prevention study (PREDIMED trial (Prevención con Dieta Mediterránea) published in 2013. The PREDIMED study surprised many in the medical community by demonstrating just how effectively the Mediterranean diet (supplementing with either increased intake of olive oil or mixed nuts) can prevent cardiovascular disease, compared to a low-fat diet.9 The results of the PREDIMED trial are comparable to Bao's study in that they demonstrated that individuals eating nuts more than three times per week died less often from cardiovascular disease and cancer than those who did not consume nuts.10 Though encouraging, PREDIMED was limited by a median follow-up of only 4.8 years and a smaller sample size. Accordingly, one of the strengths of Bao's study is a large sample size and longer duration of follow-up.
So which nuts should we be eating? Tree nuts are the most common type of nut studied for health benefits. Tree nuts are defined as dry fruits with one seed in which the ovary wall becomes hard at maturity.2 The most popular tree nuts include almonds (Prunus spp.), Brazil nuts (Bertholletia excelsa spp.), cashews (Anacardium occidentale), hazelnuts (Corylus avellana), macadamia nuts (Macadamia spp.), pecans (Carya illinoinensis), pine nuts (Pinus spp.), pistachios (Pistacia vera), and walnuts (Juglans regia).7 Consumers often erroneously identify peanuts (Arachis hypogaea) as nuts, but they are actually legumes.7 Peanuts do, however, have a similar nutrient profile as tree nuts.11 Of note, chestnuts (Castanea sativa) are tree nuts as well, but they are generally excluded from the category of "healthy" tree nuts because they are much starchier and have a less favorable nutrient profile.2
Many components of tree nuts are responsible for their nutritional value: macronutrients (fat, protein, and carbohydrates), micronutrients (minerals and vitamins), fat-soluble bioactives (monounsaturated fatty acids, polyunsaturated fatty acids, tocopherols, etc.), and bioactive phytochemicals (primarily phenolic acids and carotenoids). Additionally, tree nuts have antioxidant effects, free radical scavenging activity, and anticarcinogenic and antimutagenic effects.7 Interestingly, a study performed in 2008 compared the antioxidant and antiproliferative properties of common nuts and found that walnuts have the highest total phenolic and flavonoid contents.12
One potential limitation of Bao's study is that there was no differentiation between which specific nuts were consumed. In his study, nuts were differentiated into three categories: "peanut," "tree nut," or "any nut," which included both tree nuts and peanuts. While the nutrition profile for nuts is similar overall, each type of nut has varying levels of caloric value, different types of fat, different mineral and vitamin content, and many more factors. In the PREDIMED study, the nut-consuming intervention arm was actually divided into groups: a "walnut" arm (containing polyunsaturated fatty acids and polyphenols) and an "almonds and hazelnuts" arm (containing monounsaturated fatty acids and polyphenols).9
Another possible limitation of this study is that participants were not required to recall how the nuts they consumed were prepared (roasted, salted, etc). Of course there is a huge variety in nut preparation. Interestingly, when evaluating raw vs roasted nuts, it seems roasting does not affect the nutrition profile of the nut. On the other hand, the question of salted vs unsalted nuts leans more favorably toward the unsalted variety, as increased salt can cause harm to those with high blood pressure or other chronic cardiac conditions.
How can we encourage our patients to eat more nuts? First, reframing nuts as unique, nutrient-dense nourishment that cannot be found in other foods could encourage individuals to incorporate more nuts into their daily diet. Historically, traditional "food pyramids" or "MyPlates" sponsored by the USDA as a guide to daily nutrition have grouped nuts under the larger "protein" category as part of a meal.13 However, approximately 60% of nuts consumed in the United States are consumed as snacks.14 Thus, in an effort to encourage nut consumption in the public, it may be worthwhile for health care providers to reframe the use of nuts as "healthy snacks," and perhaps in the future, to move nuts to their own dietary category.
Overall, Bao's study impressively demonstrates an inverse relationship between those who consume nuts and all-cause mortality and mortality from heart disease. Health care providers should emphasize that any nut is a good nut (including peanuts!) as nutrient profiles overall are very similar. And it seems more nuts are better than fewer nuts. So how many nuts should one eat? Bao's study described a portion of nuts as 28 g (1 oz), whereas the FDA suggests a daily dose of 43 g (1.5 oz). Regardless of the size of one's hand, it seems to safe assume a "healthy handful" of nuts a day should be a friendly reminder to any individuals to promote health and wellness. Do NUT forget it!
References
- Kris-Etherton PM, et al. The role of tree nuts and peanuts in the prevention of coronary heart disease: Multiple potential mechanisms. J Nutr 2008;138:1746S-1751S.
- Ros E, et al. Nuts and berries for heart health. Curr Atheroscler Rep 2010;12:397-406.
- Bao Y, et al. Association of nut consumption with total and cause-specific mortality. N Engl J Med 2013;369:2001-2011.
- Mattes RD, et al. Impact of peanuts and tree nuts on body weight and healthy weight loss in adults. J Nutr 2008;138:1741S-1745S.
- Rajaram S, Sabaté J. Nuts, body weight and insulin resistance. Br J Nutr 2006;96(Suppl 2):S79-S86.
- NutHealth.org. FDA approves the first qualified health claim: Tree nuts and heart disease prevention take the lead. Available at: www.nuthealth.org/press-room/fda-approves-the-first-qualified-health-claim-tree-nuts-and-heart-disease-prevention-takes-the-lead/. Accessed Feb. 24, 2014.
- Alasalvar C, Shahidi F, eds. Tree Nuts: Composition, Phytochemicals and Health Effects. Boca Raton, FL: CRC Press; 2009.
- Ros E. Health benefits of nut consumption. Nutrients 2010;11:652-682. doi: 10.3390/nu2070652.
- Estruch R, et al. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med 2013;368:1279-1290.
- Guasch-Ferré M, et al. Frequency of nut consumption and mortality risk in the PREDIMED nutrition intervention trial. BMC Med 2013;11:164.Doi: 10.1186/1741-7015-11-164.
- Brufau G, et al. Nuts: Source of energy and macronutrients. Br J Nutr 2006;96:S24-S28.
- Yang J, et al. Antioxidant and antiproliferative activities of common edible nuts and seeds. LWT Food Sci Tech2009: 42:1-8.http://dx.doi.org/10.1016/j.lwt.2008.07.007.
- U.S. Department of Agriculture. Center for Nutrition Policy and Promotion. MyPlate. Available at: www.cnpp.usda.gov/MyPlate.htm. Accessed Feb. 28, 2014.
- King JC, et al. Tree nuts and peanuts as components of a healthy diet. J Nutr 2008;138:1736S-1740S. Presented at the conference ''2007 Nuts and Health Symposium'' held in Davis, CA, February 28-March 2, 2007.
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